Purification of aromatic hydrocarbons



Dec. 23, 1969 N J. H. DA-VIS 3,485,884

PURIFICATION OF AROMATIC HYDROCARBONS Filed April 12, 1967 DTSTILLATION\ AROMATIC HYDROCARBON 22 '8 TREATED ARQMATIC FRANK)" HYDROCARBON coumnm; H 13 ZONE l CLAY 1051mm; Q 2 zone HEAVY mcnons 60 I T l l 0m TREATINCI 0F BENZENE TO REMOVE 55 omm s L 5 -0000000051 2; 45 'ss.s PARTS FRESH cm CATALYST, -00 m0 1 CL L mum PHASE: 450F.,450 PS|C,2V/V/HR.D0WNFL0W/ *BR.|N0. TOTAL FEED I8! I Z 30 -00. |-0.0-95% 0/H FEED-=80 w Z 25 L C QWQ f 5 mm 00 1 21 1 30- Q 0 3 20 0 g 0100 0/1 0 CAPACITY w I0 03* l Q L T z 0 I000 2000 5000 4000 5000 e000 1000 0000 9000 1000 0000 BARRELS 0F FEED PER TON 0F CLAY i L 1 L L L CONDITIONS:

90.36 PARTS NICKEL CATALYST, l0'20 MESH TTT LIQUID PHASE: 450F.,450PS|G. .$MV 2030 LB/HR. F1

FEED 00502505 0001010 INC PPM THICPHENE PPM THICPHENE IN PRODUCT T M THIOPHENE IN PRODUCT 'I 'ALL'50.5 PP

BARRELS 0F FEED PER I00 LBS. 0F CATALYST INVENTOR.

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United States Patent U.S. Cl. 260-674 11 Claims ABSTRACT OF THE DISCLOSURE Aromatic hydrocarbons, such as benzene and the like, contaminated with olefins and sulfur compounds, are purified by treating the aromatic hydrocarbons in sequence with a clay such as aluminum silicate at an elevated temperature within the range of about 400 to about 500 F., followed by distillation to recover an overhead fraction which is subjected to contact with a supported nickel or nickel sulfide catalyst at a temperature within the range from about 300 to about 450 F.

BACKGROUND OF THE INVENTION Field of the invention The present invention is directed to the purification of aromatic hydrocarbons. More particularly, the invention is concerned with purification of aromatic hydrocarbons in a particular sequence of operations. In its more specific aspects, the invention is concerned with treatment of an olefin and sulfur contaminated aromatic hydrocarbon in a sequence of treating steps involving contact with clay, distillation, and contact of an overhead fraction from the distillation with a nickel or nickel sulfide catalyst.

Description of the prior art It is known to desulfurize aromatic hydrocarbons such as benzene using nickel or nickel sulfide catalyst under particular conditions. It is also known to treat aromatic hydrocarbons with clay to polymerize polymers followed by distillation to remove the polymer. However, heretofore it has not been known that olefin and sulfur containing aromatic hydrocarbons must be purified in a particular sequence where contact with a nickel or nickel sulfide catalyst must follow distillation. Thus if the aromatic hydrocarbon is treated with clay and nickel or nickel sulfide followed by distillation or not treated with a nickel or nickel sulfide catalyst in accordance with the present invention, an unsatisfactory product is obtained. Prior art considered with respect to the present invention is represented by the following listed US. Patents 1,897,798, 2,232,761, 2,311,189, 2,394,751, 2,733,286, 2,744,942 2,778,863.

SUMMARY OF THE INVENTION The present invention may be briefly described as involving a processing sequence for aromatic hydrocarbons such as benzene and the like. In the practice of the present invention an aromatic hydrocarbon fraction contaminated with olefins and at least one sulfur compound is contacted with a clay such as aluminum silicate at a temperature within the range of 400 to 500 F. This contacting operation is believed to cause alkylation of olefins with a portion of the aromatic hydrocarbons to form heavier products. The aluminum silicate contacted aromatic hydrocarbons is then distilled overhead to recover a distilled fraction amounting to about 85 to about 97 per volume of the contacted fraction. Thereafter the distilled fraction is contacted with a supported nickel or nickel sulfide catalyst in the absence of hydrogen. The nickel sufide catalyst contains from about 1 to about 3% ond contacting a substantially purified hydrocarbon which does not have to be distilled.

FEEDSTOCK AND OPERATING CONDITIONS The feedstock of the present invention is an aromatic hydrocarbon fraction which is contaminated with a small amount of olefins and at least one sulfur compound. The aromatic hydrocarbon fraction is preferably substantially benzene, but may also be toluene, Xylenes, any one of the xylenes, durene, and other tetra-methyl benzenes. Other aromatic hydrocarbons may also be suitably purified. The olefinic hydrocarbons making up part of the impurities may boil in the range of the aromatic hydrocarbons. The sulfur compounds may suitably include by way of illustration and not by way of limitation thiophene, hydrogen sulfide, disulfides and other organic sulfur compounds found in aromatic hydrocarbon fractions which may be of petroleum origin but not limited thereto.

The catalyst employed in the present invention is suitably a nickel supported catalyst or a nickel supported catalyst which contains from about 1% to about 3% by Weight of sulfur. Ordinarily the catalyst will contain from about 1% to about 2% by weight of sulfur. The nickel sulfide may be Ni S The catalyst may contain from about 20% to about nickel on a suitable support such as but not limited to kieselguhr and the like. The nickel sulfide catalyst contains from about 1% to about 3% by weight of sulfur. A preferred catalyst contains 58% by weight of nickel on kieselguhr and the fresh catalyst may be free of sulfide.

The clay employed in the first contacting operation may suitably be commercially available clays known to the trade as Filtrol clay and the like. These clays are predominantly aluminum silicate. Other catalysts such as Attapulgus clay and the like may be used. The contacting operation with aluminum silicate may be conducted at temperatures within the range from about 400 to about 500 F., pressures within the range from about 400 to about 500 p.s.i.g., and space velocities within the range from about 0.5 to about 5.0 v./v./hour.

The second contacting operation of the distilled fraction may be conducted at a temperature within the range from about 300 to about 450 F., a pressure within the range from about 0 to about 750 p.s.i.g., and at a superficial mass velocity (SMV) in pounds per square foot per hour Within the range from about to about 4,000, and in the absence of hydrogen. Hydrogen must be excluded in the second contacting operation even when using a nickel sulfide catalyst to produce pure aromatic hydrocarbons.

BRIEF DESCRIPTION OF THE DRAWING The present invention will be further illustrated by reference to the drawing in which:

FIGURE 1 is a flow diagram of a preferred mode;

FIGURE 2 is a graph of data to illustrate the clay treatment of benzene to remove olefins; and

FIGURE 3 is a graph of data illustrating the removal of thiophene from benzene with a nickel catalyst.

DESCRIPTION OF THE PREFERRED EMBODI- MENTS RELATIVE TO THE DRAWING The present invention will be further illustrated by reference to the drawing which illustrates a preferred mode. Referring now to FIGURE 1, numeral 11 designates a charge line by way of which a benzene-rich feed boiling within the range from about to about 500 F. and containing about 85 to 97% per volume of benzene is introduced into a clay treating zone 12 from a source not shown. Clay treating zone 12 contains a body or bed of aluminum silicate clay. Conditions prevail in clay treating zone 12 to remove substantially olefins contaminating the aromatic hydrocarbon fraction by reaction with a portion of the aromatic hydrocarbon. The contacted or treated product from zone 12 is discharged therefrom by line 13 which introduces the contacted product directly into a distillation zone 14 which is illustrated as a single distillation tower but which may comprise a plurality of distillation towers as may be desired. Distillation zone 14 is provided with a heating means illustrated by steam coil 15 for adjusting of temperatures as may be required, and is provided with an overhead line 16 and a bottom line 17. Heavy fractions, including alkylated reacted olefinic material, are discharged by line 17 for further treatment or recovery as may be desired. Taken overhead by line 16 is a fraction comprising from about 85 to 97% by volume of the contacted fraction charged by line 13. This fraction contains sulfur compounds of a nature described before which must be removed to make an acceptable product. These sulfur compounds are removed by introducing the distilled overhead fraction by line 16 into a contacting zone 18 which contains a body or bed of nickel or nickel sulfide catalyst of the nature described before. Contacting is provided in zone 18 to remove the sulfur and to allow recovery by line 19 of a treated aromatic hydrocarbon fraction. It is desirable that the aromatic hydrocarbon fraction such as benzene has a total sulfur content of approximately 0.5 part of a million, a thiophene content of 0.5 part of a million, and contains only a small quantity of olefins as indicated by Bromine Index of approximately 5.0. This product, a finished benzene meeting the specifications and comprising 998+ percent by volume benzene, is obtainable in accordance with the present invention.

In order to illustrate the invention further, a benzenerich feedstock containing olefins as indicated by a Bromine Index of 133 is subjected to clay treating at a space velocity f 2 v./v./hour, a temperature of 450 F., and a pressure of 450 p.s.i.g. The Bromine Index of the treated product is 22 and this product is distilled to obtain a 95% overhead fraction. This 95% overhead product has a Bromine Index of less than 5.0. The 95% overhead fraction is submitted to treatment with a nickel catalyst at a temperature of 350 F., 300 p.s.i.g., and a superficial mass velocity of 2,830 pounds per hour per square foot. The sulfur content of the finished benzene is .24 part per million and the thiophene content is 0.33 part per million.

In contrast to this operation, the same fraction and the same feedstock are supplied to clay treating under the same conditions, nickel treating under the same conditions with the same catalyst, and distilled to recover a 95 overhead product. This product contains 35 parts per million of thiophene and 12 parts per million of sulfur.

This comparison illustrates the unobvious results obtainable in the practice of the present invention.

Referring now to FIGURE 2 wherein conditions are given for treatment of a benzene fraction containing olefins, it will be seen that the Bromine Index of the product rises sharply after about 7,000 barrels of feed per ton of clay. Also FIGURE 2 shows for the 0.95 overhead fraction a sharp break at 6,700 barrels per ton of clay, which indicates that the clay is then no longer suitable for removal of olefins and must be regenerated under the following conditions: 8501,000 R, free 0 containing gas, until removal of C by burning i esSentially complete as measured by absence of CO in exit gas at end of regeneration. For example, regeneration is essentially complete when the carbon content on the clay is about 0.1 to about 0.8% by weight.

With reference to FIGURE 3, it will be clear that there is a sharp break at about 360 barrels of feed per 100 pounds of catalyst, which indicates at this point the nickel catalyst must be regenerated or replaced.

This may be accomplished in accordance with the present invention by contacting the catalyst with hydrogen at a temperature within the range from about 700 to about 950 F., at a pressure within the range from about to about 750 p.s.i.g., and at a hydrogen feed rate within the range from about 3 to about 10 standard cubic feet per pound of spent catalyst per hour until a sufficient amount of hydrogen sulfide has been removed from c spent catalyst to reduce the sulfide content to an amount within the range from about 1% to about 3% of sulfur on the catalyst. Thereafter the regenerated catalyst may be used in contacting additional amounts of the overhead fraction. Fresh nickel catalysts may be used for long periods of time. Sulfided catalysts ordinarily may be used for substantial lengths of time also without regenera'ion.

The present invention is quite important and useful in that heretofore it was not known that a sequence of operations such as described and claimed here was necessary to provide a substantially purified aromatic hydrocarbon fraction. It was also not realized that by interposing a distillation operation between a clay treating and a particular nickel or nickel sulfide treating operation, a purified aromatic hydrocarbon could be obtained which would not require subsequent distillation. The nature and objects of the present invention having been completely described and illustrated and the best mode contemplated set forth, what I wish to claim as new and useful and secure by Letters Patent is:

What is claimed is: 1. A method for treating an aromatic hydrocarbon fraction which comprises the steps in the order named of:

contacting an aromatic hydrocarbon fraction contaminated with olefins and sulfur compounds with aluminum silicate at temperature within the range from about 400 to about 500 F.;

said contaminating olefins boiling in the same boiling range of the aromatic hydrocarbon fraction;

distilling overhead from said contacted fraction from about to about 97% to recover a distilled fraction;

contacting said distilled fraction with a supported nickel catalyst in the absence of free hydrogen under conditions including a temperature within the range from about 300 to about 450 F.; and recovering from said second contacting step a substantially purified aromatic hydrocarbon fraction,

2. A method in accordance with claim 1 in which the supported nickel catalyst is a nickel sulfide catalyst containing from about 1% to about 3% by weight of sulfur a5 Nl3S2,

3. A method in accordance with claim 1 in which the nickel catalyst contain 58% by Weight of nickel.

4. A method in accordance with claim 1 in which the aromatic hydrocarbon fraction is contacted with alu minum silicate at:

(a) a pressure within the range from about 400 to about 500 p.s.i.g.; and

(b) a space velocity within the range from about 0.5

to about 5.0 v./v. hour.

5. A method in accordance with claim 1 in which the distilled fraction is contacted with a supported nickel catalyst at:

(a) a pressure Within the range from about 0 to about 750 p.s.i.g.; and

(b) a superficial mass velocity in pounds per square foot per hour within the range from about 100 to to about 4,000.

6. A method in accordance with claim 1 in which the aromatic hydrocarbon fraction is contacted with aluminum silicate at:

(a) a pressure within the range from about 400 to about 500 p.s.i.g.; and

(b) a space velocity within the range from about 0.5

to about 5.0 v./v./hour, and in which the distilled fraction is contacted with a supported nickel catalyst at:

(a) a pressure within the range from about 0 to about 750 p.s.i.g.; and

(b) superficial mass velocity in pounds per square foot per hour within the range from about 100 to about 4,000.

7. A method in accordance with claim 6 in which the supported nickel catalyst is initially free of nickel sulfide.

8. A method in accordance with claim 6 in which said second contacting operation is continued until said supported nickel catalyst becomes contaminated to the extent that sulfur compounds appear in the product, and then said contaminated catalyst is regenerated by contacting said contaminated catalyst with hydrogen at a temperature within the range from about 700 to about 950 F., at a pressure within the range from about 75 to about 750 p.s.i.g., and at a hydrogen feed rate within the range from about 3 to about standard cubic feet per pound of contaminated catalyst per hour to reduce the sulfur content of the nickel catalyst to within the range from about 1% to about 3% by weight.

9. A method in accordance with claim 6 in which said aroma-tic hydrocarbon fraction is contacted with said aluminum silicate until said aluminum silicate becomes sufiiciently spent that olefins appear in the aluminum silicate contacted product and then said spent aluminum silicate is regenerated by burning at a temperature within the range of 850 to 1,000 F. in the presence of a free oxygen containing gas to reduce the carbon content on the catalyst to about 0.10.8% by weight.

10. A method in accordance with claim 6 in which the aromatic hydrocarbon is benzene.

11. A method for treating an aromatic hydrocarbon fraction which comprises the steps in the order named of:

contacting an aromatic hydrocarbon fraction contaminated with olefins and sulfur compounds with aluminum silicate at a temperature sutficient to remove substantially said contaminating olefins:

said contaminating olefins boiling in the same boiling range of the aromatic hydrocarbon fraction;

distilling overhead from said contacted fraction a sufficient amount to recover a distilled fraction and to remove heavy fractions formed in said aluminum silicate contacting step;

contacting said distilled fraction with a supported nickel catalyst in the absence of free hydrogen under conditions including a temperature sufficient to remove substantially contaminating sulfur compounds; and

recovering from said contacting step a substantially purified aromatic hydrocarbon fraction.

References Cited UNITED STATES PATENTS 2,951,034 8/ 1960 Stuart 5 208244 3,251,897 5/1966 Wise 260671 3,367,862 2/1968 Mason et a1. 208244 XR DELBERT E. GANTZ, Primary Examiner CURTIS R. DAVIS, Assistant Examiner US. Cl. X.R. 208--2l1 

